docs: def add_xy(self, x, y):
          """ Add an motor order/sensory effect pair to the model
  
              :arg x:  an input (order) vector compatible with self.Mfeats.
              :arg y:  a output (effect) vector compatible with self.Sfeats.
          """
          self.imodel.add_xy(self._pre_x(x), self._pre_y(y))